roof and wall vents study under simulated hurricane winds · the design for the 6-fan wow consisted...

A Resource for the State of Florida

HURRICANE LOSS REDUCTION

FOR

HOUSING IN FLORIDA:

Roof and Wall Vents Study under

Simulated Hurricane Winds

A Research Project Funded by The State of Florida Division of Emergency Management

Prepared by:

Dr. Arindam Gan Chowdhury, Assistant Professor

Peeyush Kawade & Tuan-Chun Fu, Graduate Research Assistants

Department of Civil and Environmental Engineering

Florida International University

In Partnership with:

The International Hurricane Research Center

Florida International University

September 2009

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TABLE OF CONTENTS

CHAPTER PAGE TABLEOF CONTENTS……………………………………………………….. - 1 -

1. INTRODUCTION AND BACKGROUND …………………………….. - 2 - 2. TEST METHODOLOGY ……………………………………………….. - 5 - 3. THE WoW TESTING APPARATUS…………………………………… - 6 - 3.1 Full scale testing equipment (Wall of Wind)…………………….. - 7 - 3.2 WoW flow management techniques……………………………… - 9 - 3.3 Water Injection System…………………………………………... -12 - 4. EXPERIMENTAL APPROACH……………………………………….. - 14 - 4.1 Roof and Wall Vents Setup and Instrumentation……………… - 16 - 4.1.1 Pressure Testing………………………………………….. - 17 - 4.1.2 Water Intrusion Testing………………………………….. - 20 - 4.2 Experimental Procedure………………………………………... - 23 - 4.2.1 Pressure Testing…………………………………………… - 23 - 4.2.2 Water Intrusion Testing………………………………… - 24 - 5. RESULTS AND DISCUSSION………………………………………… - 26 - 5.1 Pressure Test Results ……………………………………………. - 26 - 5.1.1 Gable Roof Results…………………………………….. - 27 - 5.1.2 Visualization of Turbine Pressure Coefficients for Gable Roof……………………………………………...-32 - 5.1.3 Hip Roof Results………………………………………….. - 36 - 5.2 Water Intrusion Test Results……………………………………. - 41 -

5.3 Influence of Reynolds Number on Pressure Distribution over Cylindrical Vent with Circular Cross Section (Turbine Vent)……. - 47 -

5.4 Uplift and Drag Coefficients……………………………………... - 50 - 5.4.1 Uplift Coefficients…………………………………….. - 50 - 5.4.2 Drag Coefficients…………………………………………. - 51 - 6. CONCLUSIONS………………………………………………………… - 53 - 7. REFERENCES AND RELATED LINKS ...…………………………… - 56 -

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1. INTRODUCTION AND BACKGROUND

Natural hazards such as earthquakes, landslides, lightning, floods, windstorms and

tsunamis, are great threats to the mankind. Such disasters cost high risk to people and

their property. Natural disasters can cost billions of dollars in recovery and repairs. The

biggest threats among all such hazards are hurricanes (NSB, 2007; Lott and Ross, 2006).

According to the Insurance Information Institute, the 2005 Hurricane Season resulted in $

57.7 billion dollars in insured losses. A large portion of these losses was attributed to roof

damage. Since the mid 1990s the North Atlantic Basin has experienced a substantial

increase in tropical cyclone activity fueled primarily by warmer than usual sea surface

temperature and decreased wind shear. Goldenberg et al. (2001) concluded that the years

1995-2000 saw the highest mean number of major hurricanes and mean Net Tropical

Cyclone (NTC) activity of any 6 consecutive years in the entire 1944-1995 database. The

2004 hurricane season also proved record breaking with four storms affecting the same

state, namely Florida, in one season; the last time four storms impacted one state was in

1886 when Texas endured four direct hits. Proportional with increased frequency in

hurricane landfall is the increase in damage of economy, destruction of built environment

structures (mainly roof structure of residential buildings) and loss of life.

The number of major hurricanes and the annual number of named storms has been

shown in Figure 1. It appears that in last 3 decades there is an increasing trend in the

occurrence of storms, which together with a growing coastal population presents a new

challenge for the Civil and Wind engineering communities. According to the Annual

Summary for the Atlantic Hurricane Season 2004 (National Hurricane Centre), losses due

to hurricanes in the 2004 season were estimated to be $ 45 billion and they also

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accounted for 3100 casualties, 60 of which happened in the United States (Frankling et

al., 2005). The growth of hurricane-induced losses from $1.3/year pre-1990 to $36B/year

post-2000 is a direct result of over 50 years of accumulated socio-economic decisions to

invest in physical infrastructure and community development along coastlines, where

now 50% of the US population lives within 50 miles of the seaboard (National Academy

of Sciences, 1999). The 2005 Hurricane season also produced strong storms with

devastating power, such as Wilma and Katrina, causing losses over $ 100 billion. The

magnitude of the storms can’t be changed, but the magnitude of the impact on population

and damages caused by them might be minimized by improving construction techniques

and materials and by increasing the general awareness of the risks imposed by this natural

phenomenon.

Figure 1. Annual number of named storms (BLUE) and major hurricanes (RED) 1944-2005 (source: National Climatic Centre, 2006)

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Roof and Wall Ventilation:

Typical household activities can cause serious problems to a roof and attic if

proper roof ventilation is not provided. For example, in summer, heat build-up

encourages the premature aging and cracking of wood and other roofing materials.

Unwanted heat also can transfer back down into living areas – which reduces energy

efficiency. Similarly, in cold weather, warm air generated by laundry, showers, dish

washing and cooking can linger in the house and cause moisture build-up. The only way

to combat these problems is to have a balanced ventilated wall and roofing system. That

means it’s important to have proper ventilation, plus the appropriate amount of attic

insulation to maximize performance.

In a balanced system, wind blowing over the ridge creates negative pressure that

draws the warmer air out of the attic. Replacement air then enters through underside of

the eave or soffit vents, bathes the underside of the roof, and exits through ridge, roof or

gable vents. Even without wind, the natural convection action of rising warm air

maintains a continuous airflow along the underside of the roof.

Proper ventilation—along with attic insulation—helps maintain a comfortable

temperature inside a home, increase energy efficiency, prevent moisture damage and

contribute to the longevity of a roof. However the vents are subjected to wind loading and

can be the path for water infiltration during hurricane events. Very limited research has

been performed on water intrusion through various types of vents under differential

pressures. The current project focuses on the performance of vents under simulated

hurricane effects.

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2. TEST METHODOLOGY:

Florida Building Code (FBC, 2007 – Section 1523) defines the minimum testing

requirements for substrates, roofing components, roofing systems and roofing assemblies.

The current study is based on full-scale holistic testing of roof vents which provides

advantages over component testing as the whole building structure incorporated with

vents is subjected to wind and wind-driven rain field engulfing the structure and thus

producing realistic aero-hydrodynamic effects. A full-scale model representing a typical

low-rise building was constructed for the testing purpose. Roof and wall vents were

installed on the building model. Wall of Wind (WoW) (6-fan system) was used to

determine wind forces and water intrusion through the vents. Pressure differentials for

the vents were obtained from a simultaneous project (Bitsuamlak and Tecle, 2009).

Transducers installed on the vents measured the wind-induced loading and data was

acquired using the lab view data acquisition software.

Tests were performed with and without wind-driven rain. Any failure mode

and/or water intrusion was recorded. Failure modes of and water intrusion through

different kinds of vents were studied and correlated to the wind speed and wind-driven

rain intensity. This research provides information that will help to address significant

vent damage and secondary water infiltration and debris generation occurring related to

the poor performance of roof and wall vents.

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3. THE WALL OF WIND (WoW) TESTING APPARATUS:

3.1 Full scale testing equipment -- Wall of Wind (WoW) Built by the International Hurricane Research Center (IHRC), the Wall of Wind

(WoW) hurricane simulator is a full-scale destructive testing apparatus located at FIU’s

Engineering Center Campus. This machine is capable of testing a full-scale low-rise

building model. The WoW comprises of a 6-fan array and was used for this study. In its

original configuration, the 6-fan WoW had the capability of generating 125 mph wind

speeds at the exit of the contraction, corresponding to a middle range Category 3

hurricane as defined by the Saffir-Simpson hurricane intensity scale (Huang et al., 2009).

This integrated system couples hurricane like winds with wind-driven rain in a controlled

environment to allow realistic simulation of hurricane wind and rain interactions with

buildings (Bitsuamlak et al., 2009).

The design for the 6-fan WoW consisted of six individual fan modules. Figure 2a

& 2b shows the 6-fan WoW front view and side view. The cross-sectional area of one fan

module measured 2.44 m (8 ft) high x 2.44 m (8 ft) wide, and these six modules were

stacked into a 2x3 array, giving the 6-fan WoW a total flow field measuring 4.8 m (16 ft)

high by 6.7 m (22 ft) wide. The engine frames were designed and built to contain

carbureted Chevrolet 502 big block crate engines (Figure 3). Century Drive System SH3

2:1 counter rotating drive units were mounted to each engine, with a set of 4- bladed

Sensenich composite airboat propellers installed on the front propeller hub (closest to the

engine) and a set of 3-bladed Sensenich composite airboat propellers installed on the rear

propeller hub (farthest from the engine). The counter rotating setup was made because it

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reduces the amount of propeller-generated swirl in the flow, and it reduces the overall

propeller torque on the engine. Figure 4 a, b & c shows the setup of fans and blades and

different components of WoW relevant to the present testing.

Figure 2. Six-Fan Wall-of-Wind (a) Front View (b) Side View

Figure 3. Chevrolet 502 big block crate engines

(a) (b)

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(a)

(b) Figure 4. (a) Setup of fans and blades, (b) Control System for the fans and (c) Planks Setup

(c)

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3.2 WoW flow management techniques Passive Controls: Passive controls include (1) a contraction all around the 6-fan system used to

point the generated wind towards the test model (Figure 2 a, b); (2) an outer frame

installed outside the 6-fan WoW model acting more like a bell-mouth; (3) raising the full-

scale six fans by 0.41 m (16 in) above the ground to create a wind speed gradient at the

bottom, thus simulating an Atmospheric Boundary Layer (ABL) like flow; and (4)

installing five horizontal planks with different inclinations to increase the wind speed

with increasing height and generate an ABL-like flow. The three bottom horizontal

planks were used to redirect the flow from the bottom fans to the top fans. To optimize

the locations and inclinations of the planks, series of experiments were carried out. The

optimal configuration was determined with the planks located at the heights of 40 in, 70

in, and 94 in (1.016 m, 1.768 m and 2.376 m) with the inclinations of -0.5 0 (pointing

down), 170 (pointing up), and 170 (pointing up), respectively. Two additional planks

were installed in the upper area to improve the flow. A series of combinations of plank

locations and angles were tried to produce the targeted ABL-flow. The configuration with

five planks (i.e.; -0.50, 170, 170, 00 and 00 inclination with centers at z= 40, 70, 94, 137,

168 in, respectively) generated the target ABL profile and hence was adopted (Huang et

al., 2009).

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Active Controls: To further enhance the turbulence generation and gust effects for the WoW, rapid

variation of the fan engine speed was achieved by servo-control through multiple

sinusoidal control functions by adding low frequency fluctuations. Combinations of low-

frequency quasi-periodic waveform signals were designed based on real tropical storm

data taken from the Florida Costal Monitoring Program (FCMP), and were used to

control the rotational speed of the fans. These active controls helped to improve the

turbulence intensities as well as the power spectral densities and the gust factors. Wind

flow characteristics generated by a combination of the passive and active controls that are

used in the present study are shown in Figure 5 (Huang et al., 2009).

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Figure 5. (a) WoW Vertical shear velocity profile (b) WoW Turbulence intensity profiles for the longitudinal direction of wind

(c) Gust factors at height = 9.5 ft and z = 11 ft (d) WoW power spectral density Vs. the Kaimal and FCMP Curves

(a)

(c) (d)

(b)

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3.3 Water Injection System A steel frame was fabricated and installed in front of the 6-fan units. A grid of four

columns and three rows of Tee Jet spray nozzles, joined together with high pressure

hosing, were mounted vertically to this frame. Figure 6 a, b & c shows the steel frame

system and its details. The spray nozzles on each line were spaced 18 inches apart. In this

system, two different types of spray nozzles are used: (i) on inner lines, 8005VX nozzles

release 0.5 gallons of water per minute (0.5 gal/min) at 40 psi, (ii) on outer lines, 8003VX

nozzles that release 0.3 gallons of water per minute (0.3 gal/min) at 40 psi. A gasoline

powered pump (Figure 7) effectively works to overcome the head and preserve the water

pressure in the spray injection nozzles located on the upper rows. Water meters are used

(Figure 8) to calibrate water rate to generate a specific water rate. Water for the injection

system is stored in a 550 gallon agricultural grade horizontal leg tank (Figure 9). The

pressurized pump feeds the grid and spray nozzles, spraying the water at specified rate,

while the fans blow the wind simultaneously (Bitsuamlak et al., 2009).

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Figure 6. (a) WoW, Steel framing and setup (b) Spray nozzles used for water injection system (c) Water spray from the nozzles

(a)

(b) (c)

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Figure 7. Gasoline powered pump Figure 8. Water meter

Figure 9. 550 gallon agricultural grade horizontal leg tank 4. EXPERIMENTAL APPROACH: 4.1 Roof and Wall Vents Setup and Instrumentation

The experimental setup considered two common roof types mounted atop a 9 ft x

7 ft x 7 ft (length x width x height) building model. Prior to mounting the roof specimens

onto the building model, each roof was prepared with 30 lb felt paper underlayment

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(Figure 10 a & b), covered with 5-tab architectural shingles, and outfitted with the roof

and wall vents of interest. For the scope of this study, a 10 x 4 x 8 inch (length x width x

height) gooseneck vent, a 12-inch turbine vent, a shingle vent II ridge vent, and 16 x 6

inch soffit vents were installed on both the gable and hip roof specimens. Additionally,

the gable roof specimen contained a 12 x 12 inch rectangular gable end vent. Figure 11

shows the installation of the roof vents on the gable roof and hip roof specimens. Each of

the vents had Notice of Acceptance or Product Approval.

(a) (b)

Figure10. (a) Gable roof prepared with 30 lb felt paper underlayment

(b) Hip roof prepared with 30 lb felt paper underlayment

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Figure 11. Turbine vent, goose neck vent, and ridge vent installed on the gable & hip roof specimens

4.1.1 Pressure Testing:

A 16-channel Scanivalve Digital Sensor Array DSA 3217/16PX measured the

pressure time histories along the turbine and gooseneck vents according to the tap layout.

The Scanivalve device was installed within the attic space of the roof specimens. The

pressure taps on the turbine and gooseneck vents were created by gluing small square

tabs made of wood or hard plastic onto the inside of the vents at every pressure tap

location. Next, a 5/64 inch diameter hole was drilled out at each tap location, and a piece

of 5/64 inch outside diameter (O.D.) tubing was glued into each tap. The tubing length

between the pressure taps and the Scanivalve was no longer than three feet to minimize

signal distortion developed by the tubing. Pressure taps were also installed to measure

the external and internal pressure differential across the ridge vent, gable end vent, and

soffit vents (Bitsuamlak and Tecle, 2009). Wind attack angle and the locations of the

pressure taps on turbine and goose neck vent are shown in Figures 12 and 13. Figure 14 a

to g, shows other details related to the different vents and pressure measurement

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instrumentation. For the pressure taps installed near the soffit and gable end vents, 5/16

inch O.D. copper taps were installed. Setra 265 differential pressure transducers

measured the pressure time histories at these locations. Reference pressure tubing for

these transducers was installed in the manner described at length in Blessing (2007). The

Setra 265 pressure transducers were connected to an NI 9074 cRIO module, with NI 9205

32-channel analog voltage inputs. Figure 15 shows the NI 9074 cRIO (Compact RIO). NI

Lab View software was used to collect and record the data. All measurements were

sampled at a rate of 100 Hz during the experiments.

Figure 12. Wind angle of attack and turbine/goose neck vents locations

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Figure 13. Pressure Tap Locations: (a) Turbine (showing cross-sectional locations of

the pressure taps), (b) Goose Neck Vent

(a)

(b)

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Figure 14. (a) Pressure tubing installed within the turbine vent base (b) Pressure tap installed on gable vent (c) Turbine vent setup on the roof specimen (d) Goose neck vent setup on the roof specimen (e) Pressure tab installation on soffit vent (f) Transducer installation on soffit vent (g) Soffit vent installed on a gable roof specimen

a)

(b)(a)

(d)(c)

(e) (f)

(g)

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Figure 15. NI 9074 cRIO (Compact RIO) 4.1.2 Water Intrusion Testing:

Water intrusion tests were performed on the gable roof to quantify the volume of

water entering the attic space through each of the vents installed on the roof. A piece of

plastic sheeting was attached to the perimeter of the goose neck, turbine, ridge, and gable

end vents to contain the water entering the attic space through each vent, and direct the

water toward collection buckets for each vent. The plastic sheeting was secured with the

vents with aluminum tape, as shown in Figure 16 a to d. For the turbine and gooseneck

vents, aluminum pans were placed underneath the plastic sheeting arrangement to collect

the incoming water. For the ridge vent, a 4-inch I.D. PVC pipe was cut in half to create a

trough that would collect the water after intrusion, and direct it into eight measuring

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buckets. Plastic sheeting was installed between the ridge vent and the PVC trough to

ensure no water would bypass the collection system. A similar arrangement was

constructed for the soffit vents (Figure 16 e). Air was allowed to exit the collection pans

and the collection buckets for each vent, so that the airflow passing through the vents was

not hindered by the collection system. Figure 17 shows all the containers used for the

experiment.

Figure 16 a. Water collection setup for the gooseneck vent

Figure 16 b. Water collection setup for turbine vent

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Figure 16 c & d. Bucket setup for ridge vent and setup for gable end vent Figure 16 e. Setup for soffit vent.

Figure 17. Aluminum pan used for water collection.

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4.2 Experimental Procedure 4.2.1 Pressure Testing:

During this study, the roof vents were tested at five different angles with respect

to the WoW flow field (Figure 12): 0, 15, 45, 75, 90 degrees. A 3-minute, quasiperiodic

waveform was used to generate the wind conditions for each test (refer to Liu, 2008).

Prior to running the experiment at each angle, a 3-min baseline of pressure data

was taken. During the quasiperiodic profile, 3 min of data was collected. Following each

experiment, a second 3-min baseline was performed. All data were sampled at 100 Hz.

Both baseline datasets were used to establish the environmental conditions, and were

averaged together and deducted from the actual data collected during the WoW run to

determine the wind-induced pressure. Figures 18 and 19 show the specimen setup for

experimenting.

Figure 18. Experimental setup with turbine, goose neck and gable end vents.

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Figure 19. Experimental setup showing gable end and soffit vents. 4.2.2 Water Intrusion Testing:

For the water intrusion testing, a flow rate of 19 in/hr (maximum flow rate at

WoW) was used across the WoW flow field. The same three-minute quasiperiodic

engine waveform was used for these experiments. Once the profile was initiated, an

operator engaged the WoW water-injection system for the duration of three minutes.

After the profile was completed, the water collecting containers were removed from the

building and weighed on a digital scale. The weight of each dry container was subtracted

from the weight of the container with water to determine the amount of water intrusion

for each vent. Figure 20 shows the water intrusion test.

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Figure 20. Water intrusion test on gable roof

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5. RESULTS AND DISCUSSION 5.1 Pressure Test Results:

Figure 21 shows the time history data of typical pressure test. Each test duration

is 3 minutes for both baseline and profile parts. Coefficients (Cp) of mean and peak

pressures are calculated based on the time history data. The mean wind speed at the mid

height of the roof is used for pressure coefficients calculations.

Figure 21. Typical time history pressure data at:

(a) Windward side and (b) Leeward side

(a)

(b)

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5.1.1 Gable Roof Results:

The following figures show average, standard deviation, maximum and minimum

pressure coefficients for external pressure taps on the turbine and goose neck vents. The

maximum Cp values are obtained at the pressure taps facing the wind attack direction.

For example, for 0 degree wind attack angle, turbine tap #7 and goose neck tap #13 are

the taps facing to WoW. Therefore, the maximum Cp values were observed for #7 and #

13 windward taps.

1) For “0” degree angle of attack:

Figure 22. Cp values for “0” degree angle of attack

(a)

(b)

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a) The turbine graph (Figure 23a) shows that the maximum pressure

coefficient occurred at tap 7, having a value of approximately 2.8. Taps 5, 6, and

7 measured positive mean Cp values as they were on the windward side of the

vent. The remaining taps demonstrate suction pressure coefficients; with tap 8

having the maximum suction coefficient of -3.2.

b) The gooseneck results (Figure 23b) show the maximum pressure

coefficient occurred at windward tap 14, with a value of approximately 2.3. This

value is the maximum positive pressure coefficient on the gooseneck among all

the angles tested. Taps 12, 13 & 14, all on the windward side of the vent at 15

degrees, show positive pressure coefficients. The remaining taps experienced

suction as shown in the figure. Tap 10, located on the inclined top face of the

vent experienced the peak suction value of -3.2.


(a) (b)

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coefficient occurred at tap 6, having a value of approximately 2.8. Taps5, 6 and 7

measured positive mean Cp values, as they were on the windward side of the vent.

The remaining taps demonstrated suction pressure coefficients, with tap 1 having

the maximum suction coefficient of -3.2.


coefficient occurred at windward tap 14, with a value of approximately 2.5. Taps

12, 13 & 14, all on the windward side of the vent at 45 degrees, showed the

positive pressure coefficients. The remaining taps experienced suction. Tap 10,

located on the inclined top face of the vent experiences the peak suction value of -

3.2.


(a) (b)

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coefficient occurred at tap 5, having a value of approximately 2.3. Taps 5 & 6

measured positive mean Cp values, as they were on the windward side of the vent.

The remaining taps demonstrated suction pressure coefficients; with tap 4 having

the maximum suction coefficient of -3.1.


coefficient occurred at windward tap 12, with a value of approximately 2.9.

Taps 12, 13 & 14, all on the windward side of the vent at 75 degrees, showed


located on the inclined top face of the vent experienced the peak suction value of -

3.1.


(a) (b)

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coefficient occurred at tap 5, having a value of approximately 2.2. Taps 5 & 6

measured positive mean Cp values, as they were on the windward side of the

vent. The remaining taps demonstrated suction pressure coefficients; with

tap 4 having the maximum suction coefficient of -2.9.


coefficient occurred at windward tap 12, with a value of approximately 2.5. Taps

12, 13, 14, 15 & 16, all on the windward side of the vent at 90 degrees, show


located on the top face of the vent experienced the peak suction value of -3.1.


(a) (b)

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5.1.2 Visualization of Turbine Pressure Coefficients for Gable Roof:

a) For “0” degree angle of attack:

It appears from the graph that the gable roof does not allow a symmetric

pressure distribution around the vent. Figure 27 shows for 0 degree angle of attack

negative and positive pressure coefficients on the turbine vent. The leeward sides

of the turbine show a good symmetry where as the windward side does not.

Figure 27. Average Cp values for angle of attack at 0 degree

b) For “15” degree angle of attack:

Figure 28 shows for 15 degree angle of attack negative and positive

pressure coefficients on the turbine vent. It appears from the graph that the gable

roof specimen does not allow a symmetric pressure distribution around the vent.

The leeward sides of the turbine show some symmetry where as the windward

side does not.

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c) For “45” degree angle of attack:


pressure coefficients on the turbine vent. Similar to the earlier cases the leeward

sides of the turbine show somewhat good symmetry as compared to the windward

side.

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d) For “75” degree angle of attack:


pressure coefficients on the turbine vent.

Fig

e) Fo

Fi

pressure c

Fig

ure 30. Av

or “90” degr

igure 31 sh

coefficients o

ure 31. Av

Attack An(75 Degre

TurbineAverageCp

Attack(90 De

TurbinAveragCp

verage Cp va

ee angle of a

ows for 90

on the turbin

verage Cp va

ngleee)

e

Anglegree)

ege

2‐35

lues for angl

attack:

degree ang

ne vent.

lues for angl

0.3

‐0.63‐0.61

‐0.86

‐0.20

‐1.5

‐0.5

0.5

1.5Roof Ridg

Roof (Low

‐‐0.45

‐0.58

‐0.29

‐1.5

‐1

‐0.5

0

0.5

1

1.5

Roof R

Roof(Low

le of attack a

gle of attac

le of attack a

33

‐0.97

‐0.78

‐0.673

ge

Edge er)

0.37

‐0.76

‐0.6

‐0.54‐0.48

5

1

5

0

5

1

5

Ridge

f Edge wer)

at 75 degree

ck negative

at 90 degree

63

and positivve

2‐36

5.1.3 Hip Roof Results:

Figure 32 to 36 shows the mean, standard deviation, maximum and minimum

pressure coefficients. The pressure coefficient toward the wind direction is the greatest.

The maximum pressure coefficient value is found to be +4.0 at an angle 0 degree and the

minimum pressure coefficient occurring at an angle 0 degree is -3.9.

Figure 32. Cp values for “0” degree angle: (a) turbine vent, (b) gooseneck vent

‐6‐5‐4‐3‐2‐10123456

1 3 5 7Cp Calve

Channel

Turbine Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

‐6‐5‐4‐3‐2‐10123456

9 10 11 12 13 14 15 16Cp Value

Channel

Goose Neck Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

(a)

(b)

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‐6‐5‐4‐3‐2‐10123456

1 3 5 7Cp Valve

Channel

Turbine Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

‐6

‐5

‐4

‐3

‐2

‐1

0

1

2

3

4

5

6

9 10 11 12 13 14 15 16Cp Value

Channel

Goose Neck Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

(a)

(b)

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‐6‐5‐4‐3‐2‐10123456

1 3 5 7Cp Calve

Channel

Turbine Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

‐6

‐5

‐4

‐3

‐2

‐1

0

1

2

3

4

5

6

9 10 11 12 13 14 15 16Cp Value

Channel

Goose Neck Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

(a)

(b)

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‐6‐5‐4‐3‐2‐10123456

1 3 5 7Cp Calve

Channel

Turbine Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

‐6‐5‐4‐3‐2‐10123456

9 10 11 12 13 14 15 16Cp Value

Channel

Goose Neck Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

(a)

(b)

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‐6

‐5

‐4

‐3

‐2

‐1

0

1

2

3

4

5

6

1 3 5 7Cp Calve

Channel

Turbine Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

‐6

‐5

‐4

‐3

‐2

‐1

0

1

2

3

4

5

6

9 10 11 12 13 14 15 16Cp Value

Channel

Goose Neck Cp Value

Cp Avg

Cp Std

Cp Max

Cp Min

(a)

(b)

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5.2 Water Intrusion Test Results:

Water intrusion tests were also conducted to evaluate the performance of different

ventilation systems regarding rain water infiltration. Two water rates were used in the

gable roof water tests, one is 9 inch/hr and another one is 19 inch/hr. Only 19 inch/hr

was used for the hip roof water intrusion test. The amount of water intrusion and the

differential pressure coefficients ΔCp (difference of external and internal pressure

coefficients) are compared in this section. Figures 37 and 39 show the water intrusion

tests results. Figures 38 and 40 show the differential pressure coefficients. There was no

water infiltration through the ridge and soffit vents for gable roof. However, there was

small amount of water infiltration through the ridge vent on hip roof at 90 degree wind

attack angle. In addition, there are no significant changes in water infiltration through the

turbine vent for different wind angles.

2‐42

Figure 37. Water intrusion test results for gable roof: (a) 9 in/hr, (b) 19 in/hr

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 15 30 45 60 75 90

Water W

eight (lb

)

Wind Attack Angle

9 inch/hr Gable RoofWater Intrusion Weight vs Wind Attack Angle

Gable End Turbine Goose Neck Ridge

0

0.1

0.2

0.3

0.4

0.5

0.6

0 15 30 45 60 75 90

Water W

eight (lb

)

Wind Attack Angle

19 in/hr Gable Roof Water Intrusion vs Wind Attack Angle

Gable End Turbine Goose Neck Ridge

(a)

(b)

2‐43

Figure 38. ΔCp values for gable roof specimen vents

Figure 39. Water intrusion test results for hip roof for 19 inch/hr

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 15 30 45 60 75 90

ΔCp

Wind Attack Angle

Gable Roof Vents ΔCp vs Wind Attack Angle

Gable End Turbine Goose Neck

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 15 30 45 60 75 90

Water W

eight (lb

)

Wind Attack Angle

19 in/hr Hip Roof Water Intrusion vs Wind Attack AngleTurbine Goose Neck Ridge

2‐44

Figure 40. ΔCp values for hip roof specimen vents

Figures 37 to 40 show somewhat similar trends between the water infiltration

amount and the ΔCp values for each type of vent. This means that water intrusion

amount can be correlated to the ΔCp values. As the value of certain ΔCp increases, there

will be more water infiltration through a vent. The water amount collected by gable end

and goose neck vents varied with the wind attack angle as shown in Figures 37 to 40.

This is because both types of the vents have frontal openings. The water amount will

increase if the wind attack angle is aimed to the vent frontal openings. However, it was

observed that at “0” degree angle of attack the amount of water infiltration through the

gable end vent was not the maximum. This may be due to the mechanism of the gable

end vent. Figure 41 shows the gable end vent with the blinds. When the water came from

perpendicular direction of the vent surface, the blinds could block some amount of the

water from getting into the vent.

‐0.2

0

0.2

0.4

0.6

0.8

0 15 30 45 60 75 90

ΔCp

Wind Attack Angle

Hip Roof Ridge Vent ΔCp vs Wind Attack Angle

Turbine Goose Neck Ridge

2‐45

Figure 41. Gable end vent

Figures 42 and 43 show the ΔCp values of soffit and rigde vents on gable roof

specimen. Most of the ΔCp values are less than 0.1 and all of the ΔCp values are less

than 0.15. The low ΔCp values explain why there was no water intrusion for the soffits

and ridge vents in the gable roof tests.

Figure 42. ΔCp values for soffit vents for gable roof specimen

‐0.15

‐0.1

‐0.05

0

0.05

0.1

0.15

0 15 30 45 60 75 90Soffit ΔCp

Wind Attack Angle

Gable Roof Soffit ΔCp vs Wind Attack Angle

Left Front Right Front Left Rear Right Rear

2‐46

Figure 43. ΔCp values for ridge vents for gable roof specimen

Figure 44 shows the ΔCp values for soffit vents for the hip roof specimen. Since most of the values are negative, there will be no water intrustion for these soffit vents.

Figure 44. ΔCp values for soffit vents for hip roof specimen

‐0.15

‐0.1

‐0.05

0

0.05

0.1

0.15

0 15 30 45 60 75 90

Ridge Ve

nt ΔCp

Wind Attack Angle

Gable Roof Ridge Vents ΔCp vs Wind Attack Angle

Right Ridge Center Ridge Left Ridge

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0 15 30 45 60 75 90

Soffit ΔCp

Wind Attack Angle

Hip Roof Soffit ΔCp vs Wind Attack Angle

Left Front Right Front Left Rear Right Rear

2‐47

Figure 45 shows the ΔCp values for ridge vents on hip roof specimen. It was noticed that

there was some water coming through the ridge vent at 90 degree wind attack angle

(Figure 39 the yellow curve). Figure 45 also shows that at 90 degree wind attack angle,

the ΔCp increased to 0.6 sharply which increased the chances for water infiltration.

Figure 45. ΔCp values for ridge vent for hip roof specimen

5.3 Influence of Reynolds Number on Pressure Distribution over Cylindrical

Vent with Circular Cross Section (Turbine Vent)

Drag coefficient is a function of Reynolds number (Re) (Simiu and Scanlan,

1996). Figure 46 shows typical curve for drag coefficients Cd vs Re. In the current

pressure testing, the Re has been calculated as: Re = 67000 x V x L. Where V is the

mean wind speed at men roof height and L is the dimension of the object. In our case, L

can be considered as the diameter of turbine which is 12 inch (0.305m). Therefore, the

Re = 67000 x 20.27 m/s x 0.305m = 4.14 x 105 and the corresponding Cd value is 0.32

‐0.2

0

0.2

0.4

0.6

0.8

0 15 30 45 60 75 90

Ridge Ve

nt ΔCp

Wind Attack Angle

Hip Roof Ridge Vent ΔCp vs Wind Attack Angle Ridge

2‐48

(Figure 46). However, as the Re decreases below 4 x105, the Cd value increases sharply,

e.g., Cd = 1.1for Re=2 x 105.

Figure 46. Drag Coefficient as a function of Reynolds number (Wang, 2001)

Figure 47 shows the pressure coefficients over the turbine circumstantial surface.

Compared to the results presented by Simiu and Scanlan (1996), the data obtained from

Wall-of-Wind is close to that for Re = 1.1 x 105. In addition, the Cp values for hip roof

test are smaller than the Cp values for gable roof test.

2‐49

Figure 47. (a) Cp values distribution along turbine vent for gable roof

Figure 47. (b) Cp values distribution along turbine vent for hip roof

‐1.5

‐1

‐0.5

0

0.5

1

1.5

0 30 60 90 120 150 180

Cp

Degree

Pressure Coefficient Distribution Over Turbine (Gable Roof)

0 15 45 75 90Wind Attack Angle

‐1.5

‐1

‐0.5

0

0.5

1

1.5

0 30 60 90 120 150 180

Cp

Degree

Pressure Coefficient Distribution Over Turbine (Hip Roof)

0 15 45 75 90Wind Attack Angle

2‐50

Figure 47. (c) Cp values distribution along Circular cylinder (Simiu and Scanlan, 1996)

5.4 Uplift and Drag Coefficients

5.4.1 Uplift Coefficient

The uplift coefficients CL are also calculated for goose neck vent and shown in

Figure 48. In the figure, the CL values observed for gable and hip roofs are not only

different at the minimum values, but also the trends of the curves are quite dissimilar.

For hip roof, goose neck vent is subjected to uplift forces from all wind attack angles.

However, for the gable roof, goose neck vent is only subjected to uplift forces at 0 and 15

degree wind attack angles. At 45, 75, and 90 degree wind attack angles, goose neck is

subjected to push down forces.

‐3‐2.5‐2

‐1.5‐1

‐0.50

0.51

0 30 60 90 120 150 180

Cp

Degrees

Influence of Reynolds number on pressure distribution over a circular cylinder

(Simiu and Scanlan, 1996)6.7x10^5 1.1x10^5 8.4x10^6Reynolds Number

2‐51

Figure 48. Goose neck vent uplift coefficients for gable roof and hip roof

5.4.2 Drag Coefficient

The turbine vent drag coefficient for different wind attack angles on both gable

roof and hip roof are shown in Figure 49. For gable roof, Cd coefficient is between 0.3

and 0.75. For hip roof, the Cd value for turbine vent is about 0.3. The maximum goose

neck vent Cd value is 1.25 on gable roof and 0.75 on hip roof. It is noticed that both

turbine and goose neck vents are subjected to higher Cd values on the gable roof. For the

hip roof, the maximum Cd values of turbine and goose neck vents are about half of the Cd

values for the gable roof. By comparing the Cd values for turbine which are between 0.3

and 0.7 with the Cd values in Figure 46, the Re obtained from Figure 46 is between 3 x

105 and 5 x 105. This range includes the Re value calculated previously as 4.14 x 105 for

current testing.

‐0.7

‐0.6

‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0.0

0.1

0.2

0 15 30 45 60 75 90

C L

Wind Attack Angle

Hip Roof Goose Neck Up Lift Coefficient

Hip Roof Goose Neck Gable Roof Goose Neck

2‐52

Figure 49. Vent drag coefficients for gable roof and hip roof

0

0.5

1

1.5

0 15 30 45 60 75 90

C d

Wind Attack Angle

Gable Roof Turbine and Goose Neck Drag CoefficientsTurbine Cd Goose Neck Cd

0

0.5

1

1.5

0 15 30 45 60 75 90

C d

Wind Attack Angle

Hip Roof Turbine and Goose Neck Drag CoefficientsTurbine Cd Goose Neck Cd

(a)

(b)

2‐53

6. CONCLUSIONS:

The tests indicate that water infiltration through a vent system is dependent upon

the differential pressure as well as the vent mechanism. For vents experiencing higher

differential pressures, cost effective vent covers can be used during storms to reduce

water infiltration. Active controls can also be designed to close the vents automatically as

differential pressure increases based on the wind speed and wind angle of attack. The

later strategy is a topic of future research.

Based on the results the current full-scale test protocol developed for testing vents

seems to be an effective method to relate the water intrusion through vents to the

differential pressure across the vents. The tests generate realistic aerodynamic loads on

the holistic building models incorporated with various vents. Such aerodynamic loads

dictate the differential pressures which are the driving factors for water intrusion through

the vents. Future study should include comparison of current test protocol with that

indicated in the Florida Building Code. This will help in determining the adequacy of test

protocols given in the code and suggest necessary modifications.

Based on the test results, in general, the overall volume of water intrusion

between 0 and 30 degrees angles of attack was significantly smaller than that for angles

of attack between 45 through 90 degrees. This can be attributed to the gooseneck vent,

which allowed the most water to enter between 45 and 90 degrees. This is because the

opening on the gooseneck was facing the wind for angles of attack between 45 through

90 degrees.

The volume of water intrusion through the gable end vent for perpendicular winds

(0 degree) is less than that for slightly oblique winds (say, 15 degree) though the different

2‐54

pressure is higher for the former case. The reason behind this can be the louver

mechanism which doesn’t allow perpendicular wind or water to get into it that easily.

However at slight inclination the wind-driven rain can get through the opening under the

louver. For the gable end vent no water intrusion was seen at 75 degree and 90 degree

angles of attack and a linear trend is visible for 15 degree to 75 degree.

Water infiltration through the turbine vent is pretty much consistent and is

somewhat independent of the wind angles of attack (angles from 0 degree to 90 degree).

As the top of the turbine vent is always spinning at the time of wind attack it lessens

water intrusion through it.

For the goose neck vent a consistent trend of increasing water infiltration is

observed with the increase in the differential pressure based on the angle of attack. The

goose neck vent has maximum water infiltration when the opening on the gooseneck vent

faces the wind which allows maximum pressure differentials for angles of attack between

45 through 90 degrees. It is recommended that the goose neck vent should be covered

during storms to reduce water infiltration.

For the ridge vent differential pressure coefficient is minimal and no water

intrusion is seen for most of the angles of attack (except 90 degree for hip roof for which

differential pressure increases abruptly). Similarly, for the soffit vent no water intrusion

was seen for any of the angles of attack. This is unusual as soffit vent water intrusion had

been observed during many past hurricanes. For the current tests the roof eave inclination

might have prevented the water infiltration through the soffit vents (see Fig. 19). Further

research is needed in this area to develop methods for reducing water infiltration through

soffit vents.

2‐55

The relationships obtained between Reynolds number and the drag coefficients or

pressure coefficients were comparable with previous studies.

2‐56

7. REFERENCES AND RELATED LINKS: AIR VENT INC. [http://www.airvent.com/homeowner/whyVent/whyVent.shtml] Baffled attic Vent, Richard S. Duncan et al [http://www.google.com/patents?id=Rt6fAAAAEBAJ]

Blessing, C.M. (2007), “Mitigation of Roof Uplift Through Vortex Sup pressure Techniques” MSc Thesis, Florida International University, Miami, Florida.

Bitsuamlak, G.T., Gan Chowdhury, A., Sambare, D. (2009), “Application of a Full-Scale Testing Facility for Assessing Wind-Driven-Rain Intrusion,” Building and Environment, 44 (12), pp. 2430-2441.

Bitsuamlak, G. T., Tecle A. (2009), “Full-Scale External and Internal Pressure Measurements on Low-Rise Building Roofs,” Report submitted to IHRC, Research Project funded by The State of Florida Department of Community Affairs.

Florida Building Code 2007. Huang, P., Gan Chowdhury, A., Bitsuamlak, G. T., Liu, R., (2009), “Development of Devices and Methods for Hurricane Wind Flow Simulation in a Full-Scale Testing Facility,” Wind and Structures, 12 (2), pp. 151-177. Lott, N., and Ross, T., (2006), “Tracking and Evaluating U.S. Billion Dollar Weather Disasters, 1980-2005,” Forum on Environmental Risk and Impacts on Society: Successes and Challenges American Meteorological Society. Liu, R. (2008) “Flow Characterization and Active Control of Turbulence,” MSc Thesis, Florida International University, Miami, Florida. National Academy of Sciences. Meeting research and education needs in coastal engineering. National Academy Press; 1999. pp. 11. National Science Board (2007), “Hurricane Warning: The Critical Need for a National Hurricane Research Initiative,” NSB-06-115. Owens Corning Roofing. THE PINK PANTHER™ & © 1964-2009 Metro-Goldwyn-Mayer Studios Inc [http://roofing.owenscorning.com/homeowner/accessories/ventilation/?s_kwcid=roof%20vents%7C2522511830] Roof and Wall Venting System. Kind Code: A1. Document Number: 20080028704. [http://www.freepatentsonline.com/y2008/0028704.html?query=Wall+vents&stemming= on] Roof and Wall Venting System. Kind Code: A1. Document Number: 2007001195. Document type: United States Patent Application. [http://www.freepatentsonline.com/y2007/0011957.html?query=Wall+vents&stemming= on]

2‐57

Risk Management Solutions. [www.rms.com] Science Directory [http://www.sciencedirect.com/science?_ob=PublicationURL&_cdi=5715&_auth=y&cct=C000054271&_version=1&_urlVersion=0&_userid=2139759&_pubType=J&md5=628077b0eac596abb0913ff26b275c7f] Simiu E., Scanlan R. (1996), “Wind Effects on Structures”, 3rd edition, New York: Wiley.

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